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Bug when using pipefail and lastpipe together in bash-4.4

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  Bug when using pipefail and lastpipe together in bash-4.4 Webstrand <webstrand@gmail.com> - 2019-10-08 09:43 -0400

#15485 — Bug when using pipefail and lastpipe together in bash-4.4

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When running the following script under bash-4.4.0 to bash-4.4.23 it
seems to fail erroneously on read.

  set -x
  set -o pipefail
  shopt -s lastpipe

  main() {
    # Any input piped into while such that the condition
    # succeeds at least once.
    echo "x" | while read; do
      echo | read # anything piped to read
      sleep 0     # any non-builtin
    done
  }

  main || echo "main failed"

This produces the xtrace:

  + set -o pipefail
  + shopt -s lastpipe
  + main
  + read
  + echo x
  + read
  + echo
  + sleep 0
  + read
  + echo 'main failed'
  main failed

Under bash-4.3 and bash-5.0 the script does not output "main failed",
as expected.

I'm not sure if this is a known bug. One user on IRC reported finding
the same issue on debian stretch, but another could not reproduce the
issue for bash-4.4.12.

I have bisected the history of the devel git branch and found that the commit:
  85ec0778f9d778e1820fb8c0e3e996f2d1103b45 commit bash-20150417 snapshot
introduces the issue.

Applying the attached patch to a bash-4.4.23 source tree produces an
interpreter which does not output "main failed" when running the
aforementioned script.

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